1. Field of the Invention
The invention is related to the field of magnetic disk drive systems and, in particular, to a write element having a shaped trailing shield to improve transition curvature. More particularly, the shape of the trailing shield reduces shunting of the magnetic field by the trailing shield at the track edges to improve transition curvature.
2. Statement of the Problem
Magnetic disk drive systems typically include a magnetic disk, a recording head having write and read elements, a suspension arm, and an actuator arm. As the magnetic disk is rotated, air adjacent to the disk surface moves with the disk. This allows the recording head (also referred to as a slider) to fly on an extremely thin cushion of air, generally referred to as an air bearing. When the recording head flies on the air bearing, the actuator arm swings the suspension arm to place the recording head over selected circular tracks on the rotating magnetic disk where signal fields are written to and read by the write and read elements, respectively. The write and read elements are connected to processing circuitry that operates according to a computer program to implement write and read functions.
Magnetic disk drives have typically been longitudinal magnetic recording systems, wherein magnetic data is recorded as magnetic transitions formed longitudinally on a disk surface. The surface of the disk is magnetized in a direction along a track of data and then switched to the opposite direction, both directions being parallel with the surface of the disk and parallel with the direction of the data track.
Unfortunately, data density requirements are fast approaching the physical limits. Overall data density (or areal density) may be improved by improving linear density and/or track density. To improve linear density, bit sizes on a track need to be reduced which in turn requires decreasing the grain size of the magnetic medium. As this grain size shrinks, the magnetic field required to write a bit of data increases proportionally. The ability to produce a magnetic field strong enough to write a bit of data using conventional longitudinal write element technologies is reaching its physical limit.
One way to achieve higher density recordings is with perpendicular recording. In perpendicular recording systems, bits of data are recorded magnetically perpendicular to the plane of the surface of the disk. The magnetic disk may have a relatively high coercivity material at its surface and a relatively low coercivity material just beneath the surface. A write pole having a small cross section and very high magnetic flux emits a strong, concentrated magnetic field perpendicular to the surface of the disk. This magnetic field emitted from the write pole is sufficiently strong to overcome the high coercivity of the surface material and magnetize it in a direction perpendicular to its surface. The magnetic flux then flows through the magnetically soft underlayer (SUL) and returns to the surface of the disk at a location adjacent to a return pole of the write element. The return pole of the write element typically has a cross section that is much larger than that of the write pole so that the magnetic flux through the disk at the location of the return pole (as well as the resulting magnetic field between the disk and return pole) is sufficiently spread out to render the magnetic flux too weak to overcome the coercivity of the disk surface material. In this way, the magnetization imparted by the write pole is not erased by the return pole.
FIG. 1 illustrates a typical write element 100 adapted to write to a perpendicular magnetic recording medium 120. Write element 100 generally includes a yoke 101 comprising a write pole 102 and a return pole 104. Write element 100 also includes a coil wrapped around yoke 101 that is not shown. Perpendicular magnetic recording medium 120 includes a perpendicular magnetic recording layer 122 and a soft underlayer (SUL) 124.
When in operation, perpendicular magnetic recording medium 120 spins from left to right in FIG. 1. A magnetic flux is generated in yoke 101 due to an electrical current flowing through the coil (not shown). The magnetic flux flows through write pole 102, and write pole 102 emits a magnetic field across the write gap into perpendicular magnetic recording medium 120. The magnetic flux then flows through the SUL 124 and returns to the surface of the disk at a location adjacent return pole 104.
As the magnetic field from write pole 102 passes through perpendicular magnetic recording layer 122, the perpendicular component of the magnetic field influences the magnetization orientation of the perpendicular magnetic recording layer 122 in the direction of the magnetic field. The magnetization orientation of three bits in perpendicular magnetic recording layer 122 is illustrated as single arrows pointing up or down in FIG. 1. The areas between bits are referred to as transitions 128, which will be discussed in more detail below.
When write element 100 is writing to perpendicular magnetic recording medium 120, write pole 102 has a leading side 106, a trailing side 107, and two track sides. The two track sides are the opposite sides parallel to the page of FIG. 1, and are not shown with a reference number. Recording generally takes place from the trailing side 107 and the two track sides of write pole 102. No recording generally takes place from the leading side 106 of write pole 102. To prevent writing to neighboring tracks, side shields may be added proximate to the two track sides, which are not shown in FIG. 1. To prevent writing to neighboring bits along the track, a trailing shield 108 may be added proximate to the trailing side 107 of write pole 102. The shields shunt some of the magnetic field from write pole 102.
FIG. 2 illustrates write pole 102 and trailing shield 108 as viewed from the ABS of write element 100. Trailing shield 108 has a leading side 202 that faces the trailing side 107 of write pole 102. Leading side 202 of trailing shield 108 is separated from trailing side 107 of write pole 102 by a desired gap, such as 50 nm. The purpose of trailing shield 108 is to shunt the low frequency components of the magnetic field emitting from trailing side 107 of write pole 102. Because trailing side 107 of write pole 102 is primarily responsible for recording, trailing shield 108 helps to sharpen the field gradient of the magnetic field. The dotted line in FIG. 2 illustrates a representation of the field contour 210 of the magnetic field generated by write pole 102 and trailing shield 108 as viewed from the ABS.
Trailing side 107 of write pole 102 defines the track width of write element 100. The track edges are illustrated between write pole 102 and trailing shield 108 as right angles in FIG. 2. As is evident in FIG. 2, the field contour 210 generated by the configuration in FIG. 2 is curved at the track edges. The curvature of the field contour 210 at the track edges unfortunately results in a curvature in the transitions between bits in perpendicular magnetic recording medium 120.
FIG. 3 is a top view of a portion of a track 302 on perpendicular magnetic recording medium 120. Due to the shape of the field contour 210 generated by write element 100, the transitions 128 between bits are curved. Also shown in FIG. 3 is an example signal 304 read from track 302. The curved transitions 128 cause problems. For one, the signal 304 read back from track 302 having curved transitions has a lower amplitude A1 than a signal read from straight transitions, which reduces the overall signal to noise ratio (see also FIG. 8). Also, the signal 304 read back from track 302 having curved transitions has wider pulse widths than a signal read from straight transitions, which limits how close the transitions can be packed together to provide high density recording (see also FIG. 8).